1. Field of the Invention
The present invention pertains generally to devices, assemblies and systems for sound reproduction and/or recording, and more particularly to an audio sound apparatus which provides enhanced sound quality by maintaining one or more solid-state components at elevated temperature during sound reproduction.
2. Description of the Background Art
Before the mid-1960s, vacuum tubes were the technology used for audio amplification. Various tubes were developed for radio, television, radar, RF power, audio and specialized applications. Over several decades of design, with a limited selection of tubes, a few standard designs for audio amplification evolved. Tube power amplifiers consisted typically of a preamplifier stage to increase the voltage signal, and an output stage to provide power amplification. The output impedance of a tube amplifier without any feedback or transformers in the circuit is limited by the characteristics of tube technology to tens or hundreds of ohms. Output transformers are usually used to lower this output impedance to provide good power transfer to low impedance loads, such as loudspeakers.
The semiconductor (transistor) revolution provided immediate advantages to the power amplifier industry over existing vacuum tube systems. Semiconductor systems are small, reliable, and they dissipate far less heat than vacuum tubes. Furthermore, transistors can be low voltage devices with low inherent impedances that eliminate the need for audio output transformers. This greatly reduces potential cost, and eliminates the distortion effects and bandwidth limitations of the transformer. The majority of systems and devices which at one-time relied on vacuum tubes have been converted to semiconductors, leaving only a few vacuum tube types manufactured and in regular use, predominantly in the high-end audio field.
Despite 35 years of transistor technology, and the apparently simple task of amplifier design, there is no standardization within the industry. Audio experts have come to recognize that all audio devices have inherent distortions to which the human ear is remarkably sensitive. The conventional measures of total harmonic distortion (THD) and frequency response have proven to be inadequate in comparing one amplifier to another.
Vacuum tube systems, with their obvious drawbacks of inefficiency, heat, unreliability, size, and high impedance, still command a strong presence in the high-end audio industry. Many listeners find vacuum tube amplifiers to be more xe2x80x9ctransparentxe2x80x9d than semiconductor systems, meaning the vacuum tube systems are less prone to the type of semiconductor distortions that change the original characteristics of the music signal. The survival of the vacuum tube amplifier defies the logic of conventional engineering measurements to this day.
For the past two decades, designers of high-end audio equipment have focused on the task of trying to get solid-state (transistor) amplifiers to sound like vacuum tube amplifiers. These efforts have usually focused on the measurable distortion characteristics found in many of the older vacuum tube amplifiers. The human ear finds even-order harmonics to be inherently of a musical nature, and some favored tube amplifiers are rich in these harmonics. Despite these efforts, no designer has yet succeeded in duplicating the quality of sound generated by tube amplifiers, as evidenced by the wide variety of designs and systems that are to be found in the current market, and the continued survival of vacuum-tube products. The high-end audio music market has not shifted to one type of transistor circuitry as the best design.
The main focus of research for the audio industry has been directed toward the circuitry. Presently, most high-end manufacturers of solid-state amplifiers recommend that their equipment should be xe2x80x9cwarmed upxe2x80x9d before critical listening, but none of the makers have actually demonstrated, or even realized, that the sound quality is directly related to the thermal heating of solid-state components. The recommendation to xe2x80x9cwarm upxe2x80x9d an audio system may originate from the classical vacuum tube systems in which xe2x80x9cwarm-upxe2x80x9d was necessary for operation. Most manufacturers need to keep the external case temperatures low for safety and reliability of audio appliances, and strive to keep the semiconductors below 60xc2x0 C.
Class A amplifiers have become popular in recent years due to their enhanced sound quality. The Class A amplifiers are designed for high output-device currents which improve linearity since the devices are always conducting. In addition to increasing measured linearity, Class A amplifiers also elevate temperatures of the output devices, though this is not the stated purpose of the increased current. The consensus is that the higher the bias currents, as in the class A amplifiers, the better the sound, since the circuit becomes more linear. As the current is increased in the output stage to increase this linearity, every effort is made to keep the output device temperature low with large heatsinks. Despite these improvements, they have not enabled solid-state audio systems to obtain the same xe2x80x9ctransparencyxe2x80x9d found in vacuum tube systems. Such Class A amplifiers fail to achieve this goal because they do not raise the temperature of the output devices sufficiently, and make no attempt to raise the temperature of the other semiconductor devices in the amplifier, such as those found in the preamplifier stage.
Some of the best available amplifiers have become passive heat managers. They are provided in very large packages that do maintain an elevated temperature. Present amplifiers typically maintain the external heatsink temperature at no more than 60xc2x0 C., and the junction temperature at no more than approximately 70xc2x0 C. The external heatsink temperature must stay low for safety.
A few amplifiers contain thermal monitoring or thermal control devices to determine the temperature of output devices. These temperature monitoring devices are utilized to ensure that the components do not overheat and therefore are believed to contribute to system reliability. Other thermal control devices are designed to compensate for varying bias current caused by fluctuating temperature to maintain the signal gain relatively constant.
The present trend in the audio industry is to restrict temperatures of power devices. External heatsinks are restricted to about 65xc2x0 C. Celsius or lower in order to keep the product safe to touch. Low thermal impedances are maintained to keep the output devices as close to this temperature as possible. Inside the case of amplifiers the temperature is maintained relatively low to ensure long life of components such as capacitors, which deteriorate with increased heat. Presently, no one in the audio field has directly addressed the thermal aspect of sound quality enhancement.
There is accordingly a need for an audio system that is capable of obtaining the transparent sound quality previously found only in vacuum tube systems, while maintaining reliability. The present invention satisfies this need, as well as others, and generally overcomes the deficiencies in the background art.
The invention is an audio sound quality enhancer which provides a transparent sound quality, using solid-state devices, which was previously available only in vacuum tube audio systems. In its most general terms, the invention comprises at least one solid-state component in the audio circuit signal path, and at least one heat source configured to heat the solid-state component or components. The invention increases the sound quality of solid-state audio systems by increasing the temperature of the semiconductor components involved in sound production. By intentionally heating the semiconductor components of an audio system above standard operating temperatures, the invention delivers sound quality levels normally only associated with vacuum tube sound systems. This invention provides a new class of solid-state semiconductor audio playing and recording components wherein every device in the audio path is deliberately heated to much higher temperatures, while maintaining safe external temperatures and full reliability on other components which are sensitive to elevated temperatures.
The invention further describes an audio device comprised of solid-state semiconductors where all of the semiconductors in the audio amplifying path are actively heated to a junction temperature of at least 60xc2x0 C., more preferably at least 80xc2x0 C, and even more preferably in excess of 100xc2x0 C. The maximum temperature may be substantially above 100xc2x0 C. In fact, temperatures of at least 125xc2x0 C., at least 150xc2x0 C., and at least 175xc2x0 C. are contemplated by this invention. The semiconductor devices which are heated include small-signal devices in addition to high-power amplifying devices. Operation below the preferred temperature range results in deterioration in sound quality.
The heat source can comprise one or more thermal elements such as a conductive (or radiative) source placed in close proximity to the solid-state components. This heat source can be placed adjacent to the audio circuit board or can be an integral part of the board. Along with the differential amplifier, the output devices should also be allowed to run in excess of 80xc2x0 C., much warmer than the industry standard. The invention also demonstrates that all of the low-power preamplifier devices should also be run at temperatures in excess of 80xc2x0 C. to achieve the best performance possible. The inventor has completed experiments which indicate that raising the temperature above 100xc2x0 C. continues to improve the sound quality.
An object of the invention is to provide an increase in the sound quality of an audio device by heating the semiconductor components of an audio circuit board by heating the complete circuit board. It is preferable to specifically heat only the audio semiconductor components with a conductive heat source in order to maintain reliability of components that cannot tolerate the increased temperature. The heat source may be mounted on the circuit board or externally located in proximity to the specific solid-state components to be heated for increased sound quality.
Another object of the invention is to provide a method of sound enhancement by heating semiconductor circuitry by applying a heat source in close proximity to circuit elements to perform the heating step.
Another object of the invention is to provide a method of sound enhancement by running sufficient power through an audio device such that it heats itself. The output power devices are suited for this. They naturally produce heat, and are in large, thermally efficient packages that manage the heat well. An improvement over current technology is to increase the thermal impedance to the heatsink to allow the devices themselves to become much hotter with the same dissipation, and maintain the same external temperature.
Another object of the invention is to provide a method of sound enhancement by using a heat source comprised of a heating element or another semiconductor, or have the circuit heat itself but control it by way of a thermal heat transfer feedback mechanism.
Another object of the invention is to provide a method of sound enhancement by heating the semiconductor elements in the audio path by utilizing internal bias currents and voltages as a heat source coupled with at least one heat transfer device to control semiconductor component temperatures within a desired range.
Another embodiment for the invention is a method of heating the semiconductor elements in the audio path using at least one additional element in the semiconductor package which does not carry audio signal as a heat source. This additional element is coupled with at least one heat transfer device to control semiconductor component temperature within a desired range.
Another object of the invention is to provide an increase in the sound quality of an audio device by using external heating elements such as resistors, coupled to heat transfer devices to control temperature within a desired range.
Another object of the invention is to provide an increase in the sound quality of an audio device by isolating the semiconductor components in the audio signal path and mount them on a separate circuit board to allow thermal management thereof.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.